In an LTE (Long Term Evolution, long term evolution) communication system supporting carrier aggregation, a UE (user equipment, user equipment) measures channels of multiple downlink cells (or called as carriers) to obtain multiple downlink CSI (channel state information, channel state information). The UE needs to feed the CSI back to an eNB (evolved NodeB, evolved NodeB), and the eNB performs downlink data scheduling by using the CSI. In the prior art, cyclic CSI of one cell is merely fed back on a PUCCH (physical uplink control channel, physical uplink control channel) Format 2/2a/2b of a subframe; and CSI of different cells is fed back on different subframes through different high-level configurations. In aforementioned feedback mode adopting the PUCCH Format 2/2a/2b, the number of feedback bits supported by one subframe is 1-11 bit (bit). The aforementioned feedback mode adopting the PUCCH Format 2/2a/2b may feed back a few bits and has long feedback delay. Therefore, a scheme for cyclically feeding back CSI of multiple cells in one subframe is proposed in the prior art. For example, cyclic CSI is transmitted on a PUSCH (physical uplink sharing channel, physical uplink sharing channel); and cyclic CSI is transmitted on a PUCCH format 3, and so on. However, in the communication system adopting a carrier aggregation technology, as quantity of activated serving cells is continually changed, a type of cyclic CSI reported in one subframe is also changed; so the number of bits fed back in one subframe is continually changed. The aforementioned prior art can not meet a condition that information (such as bit number) fed back in one subframe is changed.